We shall use the evidence that we have assembled on (1) factors that affect cell attachment to substrates; (2) differential selection of epithelial cells from mixed cell populations; (3) use of non-bicarbonate buffers; (4) experience with glutamine- and bicarbonate-free autoclavable media for monolayer and suspension cultures of fibroblasts; (5) bicarbonate-free, high Na ion/K ion media for epithelial cells; and (6) hormone supplementation, to continue to design chemically defined media for primary and long-term cultures of normal and neoplastic epithelial cells. The responsiveness of each cell type to hormones and other environmental variables such as pH, osmolality, and ion balance will be examined. A principal goal will be to achieve fully autoclavable media, specific for various cells of epithelial origin, comparable to those now in use for fibroblasts. As soon as sufficient numbers of the postnatal liver cells have been accumulated, we shall compare the abilities of these cells, and the long-term cells from fetal liver, to produce serum proteins, and the degree to which the protein synthetic process is under hormonal control.